Television transmission method



Jan. 9, 1940. K. SCHLESINGER 2,186,931

TELEVISION TRANSMISSION METHOD v Filed Aug. 13, 1935 Patented Jan. 9, 1940 UNITED STATES 2,186,931 TELEVISION TRANSMISSION METHOD Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application August 13, 1935, Serial No. 36,008

In Germany September 4, 1934 v 3 Claims.

The present invention relates to television arrangements according to the method of interlaced lines and more particularly to transmitters which transmit film images, the film being intermittently moved image per image like in ordinary film projectors.

The object of the invention are simple means I Fig. 1 shows the scanning arrangement of a television transmitter according to the invention, whilst Fig. 2 is an example of a device for producing the necessary synchronizing impulses.

By means of a Geneva stop gear 20 well known in the cinematographic art the film 6 is moved only upon change of image, and then to the extent of a complete image length. Thus the film is stationary for nearly & sec., and during this time the transmission of two-part-images (frames) is executed. The part of the film within the film gate 2| is illuminated by means of a light source l8 and a mirror l9 or similar arrangements and is projected by means of the optical system l3 on the image field of an ordinary scanning disc I0 having one spiral of e. g. 90 apertures. The disc rotates at 3000 R. P. M., accordingly performing two complete revolutions per image. A photo-cell I5 arranged behind the disc i0 would record the same 90-line image twice in succession if care were not taken for the necessary displacement of the lines. This is accomplished optically by a plano-parallel plate of glass [6 of approximately 5 mm. thickness, which is, for example, by a polarized magnet l1 thrown backwards and forwards between the two positions indicated by dotted lines with a frequency of 50 per second. Accordingly the light rays are displaced at a certain amount upwards respectively downwards, each for & of a second. This amount is by adjusting the amplitude of the oscillations of IE made equal to the width of a line. The operation of the magnet is preferably performed in synchronous fashion by the alternating current which feeds the disc motor, if necessary through the medium of a phase shifter, and the magnet is so adjusted that it moves over (Cl. 178-715) l less than a line period and then remains stationary.

The described arrangement may easily be varied for a threefold or fourfold interlaced scanning or maybe replaced by another equivalent optical arrangement.

The receiver consists of a cathode ray tube provided with a line relaxation oscillator producing 90 lines per image and a frame relaxation oscillator producing frames per second. The desired interlaced image is obtained if the frame synchronizing impulses are not isochronousbut are given by the transmitter with a time displacement corresponding to a line.

Fig. 2 shows a simple arrangement on the transmitter for producing suitable impulses.

It consists in disc with two projections 86 and 81 which, performs one revolution per image change, i. e. 25' revolutions per second. The projections 86 and 8'! are not exactly opposite to each other but displaced to the extent of an angle 6 which corresponds exactly to half the period of a line. The said projections interrupt a'bundle of light which is furnished by a special light source or derived from the light source l8 (Fig. 1), directed sharply on the same and consequently upon a photo-cell (not shown). I With an arrangement of this kind there may be produced through the medium of an amplifier the desired anisochronous impulses and superposed to the image transmission. An impulse siren of this kind may be employed as auxiliary apparatus for existing systems, in which heretofore symmetrical impulses have been produced, and would immediately place existing transmitters of this kind in a position to perform transmission according to the group-displacement method, whereby all cathode ray receivers would participate in the proper fashionin a transmission of this kind if the period of their frame relaxation oscillators is increased from '25 to 50.

I claim:

1. In a television transmitter an arrangement for scanning a film, in interlaced lines comprising means for intermittently moving said film through a film gate image per image, a scanning disc having a spiral of apertures and rotating at twice the image frequency, a lens system projecting an image of said film upon the scanning area of said disc and a plano-parallel' glass plate disposed between said film and said lens system and means for turning said glass plate suddenly twice per image change by a small angle for displacing said projected image to and fro by the width of a line.

2. In a television transmitter an arrangement for scanning a film in interlaced lines comprising means for intermittently moving said film through a film gate image per image, a scanning disc having a spiral of apertures and rotating at twice the image frequency, a lens system projecting an image of said film upon the scanning area of said disc and a plano-parallel glass plate disposed between said film and said lens system and means for turning said glass plate suddenly twice per image change by a small angle for displacing said projected image to and fro by the width of a line, said means for turning the glass plate consisting of a polarized magnet fed by an alternating current of image change frequency.

3. In a television transmitter an arrangement for scanning a film in interlaced lines comprising means for intermittently moving said film through a film gate image per image, a scanning disc having a spiral of apertures and rotating at twice the image frequency, a lens system projecting an image of said film upon the scanning area of said disc and a plano-parallel glass plate disposed between said film and said lens system and means for turning said glass plate suddenly twice per image change by a small angle for displacing said projected image to and fro by the width of a line, and an arrangement for producing the necessary anisochronous impulses consisting of a light chopper rotating at the image change frequency and adapted to produce light impulses at intervals differing from each other alternately by a line period.

KURT SCHLESINGER. 

